The Martin YB-12 was a Martin YB-10 airframe modified for Pratt & Whitney R-1690-11 Hornet radial engines. These engines were slightly more powerful than the Wright Cyclones used on the YB-10 and gave the YB-12 a speed advantage of about 5 mph. Seven YB-12s were ordered in 1933 for service test and 25 more similar aircraft were ordered as B-12A.
YB-10 with engine change
TECHNICAL NOTES: Armament: Three .30-cal. machine guns and 2,260 lbs. of bombs Engine: Two Pratt & Whitney R-1690-11 Hornet radials of 700 hp each Maximum speed: 218 mph Cruising speed: 170 mph Service ceiling: 24,600 ft. Range: 524 miles with full bomb load (1,360 miles ferry range) Span: 70 ft. 6 in. Length: 45 ft. 3 in. Height: 11 ft. Weight: 12,824 lbs. gross Serial numbers: 33-155 to 33-161